1. Field of the Invention
The present invention relates to a self-ballasted fluorescent lamp, particularly, to an improvement in the arrangement of circuit boards that constitute a ballast circuit.
2. Description of the Related Art
As a conventional fluorescent lamp apparatus, e.g., a bulb-shaped fluorescent lamp has been known, including a fluorescent tube, a ballast circuit for lighting the fluorescent tube, and a case (cover) for housing the ballast circuit. JP 2000-21351 A discloses such a bulb-shaped fluorescent lamp, where a circuit board of a ballast circuit is divided into two parts and the two circuit boards are arranged in parallel to each other, so that the area of the ballast circuit is small and the size of circuit-mounted structure is reduced. Those two circuit boards are connected electrically by a cable or the like.
In the conventional bulb-shaped fluorescent lamp, the number of electronic components (hereinafter, referred to as circuit elements) required for electronic lighting is generally about 30 to 40.
In recent years, it has been desired to apply the conventional bulb-shaped fluorescent lamp to a dimmable lighting fixture. For this reason, a ballast circuit having a dimming function has been proposed, which is formed by adding the circuit elements for dimming to a conventional ballast circuit.
However, in the ballast circuit having a dimming function, the number of circuit elements is increased from two to four times that of the conventional ballast circuit by the addition of the circuit elements for dimming. Therefore, the circuit board becomes large, which in turn increases the size of the case that houses the circuit board. Consequently, the lamp apparatus itself becomes large as well.
Moreover, the dimming circuit elements to be added include circuit elements that are easily damaged by heat. Thus, those circuit elements are damaged by heat radiated from the fluorescent tube during lamp operation, making the lifetime shorter than that of the conventional lamp.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a fluorescent lamp apparatus with longer lifetime that can suppress an increase in the size of a case for housing a ballast circuit, i.e., a lamp apparatus, and prevent the thermal damage to circuit elements during lamp operation, even if the number of the circuit elements is increased like a ballast circuit having a dimming function.
A fluorescent lamp apparatus of the present invention includes a fluorescent tube, a ballast circuit for lighting the fluorescent tube, a case for housing the ballast circuit, and a holder provided at the end of the case for holding the fluorescent tube. The ballast circuit includes at least a first circuit board and a second circuit board, and the second circuit board is arranged to be substantially perpendicular to the first circuit board.
This enables the effective utilization of space in the case when the ballast circuit is housed therein. Thus, even if the number of circuit elements is increased, the above configuration can suppress an increase in the case size. In addition, the circuit elements that are affected easily by heat can be separated from the fluorescent tube.
It is preferable that the first circuit board is arranged between the holder and the second circuit board so as to be substantially perpendicular to the central axis of the case.
It is preferable that the second circuit board is arranged so that a portion of its periphery comes into contact with the first circuit board.
It is preferable that the width of the second circuit board is reduced in the direction opposite to the fluorescent tube.
It is preferable that the second circuit board is displaced from the central axis of the case.
It is preferable that circuit elements that generate heat by electrical loss are mounted on the first circuit board, while circuit elements that are affected easily by heat are mounted on the surface of the second circuit board that does not face the circuit elements generating heat by electrical loss.